The average American taxpayer can count on two big developments to affect his pocketbook this year. Taxes will be higher at first than they were in 1977, and - most likely - they'll come back down again later in the year. It's the nine months in between that may prove difficult to take.

The tax hike already has taken effect: It's the big jump in Social Security payroll taxes that began New year's Day. By an earlier act of COngress, the tax rate for employers and workers rose to 6.05 per cent - from 5.85 per cent before - ant the total wages subject to taxes climbed to $17,700, from $16,5000.

That means a $105 a year jump in the maximum payroll tax a high-salaried worker has to pay - $1,070, from the $965-a-year upper limit last year. For a worker earning $10,000 a year, the bite widens to $605 a year from $585 in 1977.Payroll taxes will rise even more sharply in 1979 and later. And if COngress ever passes the energy bill, tax burdens will rise even further - both for individuals and businesses.

The tax reduction still must be enacted: It's the $25 billion tax cut package President Carter plans to propose for individuals and business. As officials outlined the plan in December, the proposeal will contain cuts for almost every tax bracket, and a sizable reduction in corporate taxes.

There's almost no question Congress will pass the cuts. Few presidents ever have been refused a tax cut request, and 1978 is an election year to boot. The reductions are supposed to compensate for the impact of inflation in pushing taxpayers into higher brackets and to help offset the Jan. 1 payroll tax boost and energy tax increases.

The key question is the timing. Although the President first wanted to make the tax cuts effective on July 1, House and Senate leaders wasnt to postpone it until October to avoid upsetting the new congressional budget process. Carter since has acquiesced to that plan.

As a result, barring unexpected changes, the average American's tax burden is going to be significantly higer between now and October, in a nasty - albeit temporary - New Year's shock. And that doesn't include the effects of higher gasoline and fuel oil prices as a result of the Carter energy bill.

It's still somewhat uncertain how the increase will affect consumer spending. Some liberal economists are predicting the tax hikes will produce a visible "fiscal drag" on the economy in the first nine months of the year - possibly enough to make the economy grow a bit slowly than it otherwise might.

If the tax cut goes into effect in October, only about $6 billion will affect taxes in calender 1978 - barely enough to offset the $5 billion or more increase expected from the energy and Social Security bills - let alone reduce the impact of inflation on the tax system.

For their part, Carter administration economists are betting that, after an initial pullback, AMericans will begin lossening their pursestrings again as early as this spring - in anticipation of the October tax cut. But no one really is sure.

In the meantime, however, take home pay for individuals is visibly smaller, and payroll taxes for employers are decidedly larger - drawing complaints from all over the country. And state and local tax burdens for individuals and corporations also are increasing.

The new Carter tax package includes these major elements:

A $16 to $17 billion tax cut for individuals, to be achieved both by lowering existing tax rates and replacing the present $750 a dependent personal exemption with a tax credit of $249 to $250 a dependent. The shift in the personal exemption would benefit lower-income taxpayers.

The proposal would lower the present tax rates slightly from the present 14 per cent in the lowest bracket and 70 per cent at the top - in theory, a moderate cut in tax rates for every income bracket. Officials say they also hope to rejuggle the tax rates slightly to get rid of present inequities.

A two-stage cut in the corporate tax rate, reducing it from the present 48 per cent to 45 per cent in 1978 and 44 per cent in 1980. To help smaller businesses, the administration also will propose reductions in the tax rates charged companies on their first $50,000 of income.

Expansion of the present 10 per cent investment tax credit for business - designed to spur spending on new facilities - by extending as well as equipment, and by allowing firms to use the break to offset 90 per cent of their taxes rather than 50 percent.

Carter also is proposing making the 10 per cent level permanent.Congress raised it temporarily to last through 1980, when it is scheduled to revert to the previous 7 per cent level. The investment credit was enacted originally in 1964, and has been raised and lowered several times since then.

Elimination of the present 4 per cent was tax on telephone bills which was to have been phased out anyway by 1982, and reduction of the tax paid by employers to finance federal unemployment insurance benefits to 0.5 per cent of a firm's taxable payroll, from the present 0.7 per cent level.

The measure is being billed as an anti-inflation gesture, with the end to the telephone tax saving taxpayers $1.5 billion and the payroll tax cut trimming employers' tax tabs by $800 million or so. But officials concede privately neither measure actually will have that much impact.

Elimination of two major foreign tax breaks for U.S. corporations - inpresent tax sunsidy for so-called "Domestic International Sales Corporation to defer indefinitely the taxes due on foreign earnings.

A spate of modest "tax reforms" - ranging from limiting deductions for business lunches to tightening the tax treatment of real-estate tax shelters; ending the lower alternative tax on capital gains, stiffening the minimum income tax for investors with a lot of sheltered income and providing a cash subsidy to replace the tax-free status of munipals bonds.

Aides say the President also may propose other , more modest revisions, such as new breaks for small business. Carter scrapped a more comprehensive plan in the face of political opposition.

The question on the tax cuts isn't over whether the bill will pass, but on how big it will be. The lawmakers may decide either to enlarge or reduce the package - or possibly of the major elements.

Rep. Al Ullman (d-Ore), chairman of the House ways and Means Committee, said in an interview last week he favored a much smaller tax cut than the $25 billion Carter is proposing - probably only the $15 to $16 billion needed to offset the new Social Securtiy and energy tax increases this year.

The outlook for the "tax reform" proposals is for less secure. While Ullman says he will endorse some of the istration is proposing, he doesn't want to load the package up too much for fear the tax cuts will be delayed.that means only a handful of tax changes actually go through.

As a result, Carter may have to give up hopes for any serious overhaul of the tax system for the remainder of this term - a far cry from the promise of "comprehensive reform" he made on the campign stump.

Even if the lawmakers do consider a second Carter "reform" package in 1979 or 1980, most observers believe the momentum has been lost. The initial Carter goals of toughtening the tax treatment of capital gains and eliminating the double taxation of profits and dividends may be impossible to achieve.

It's hard to say just who will come out ahead in this combination of tax changes. The payroll tax bite hits proportionally harder on the poor, but because of the increase in the wage base, in dollar terms the upper-middle-in-come taxpayer may notice the increase more.

On the other hand, shifting from the present $750 personal exemption to a new $250-a-dependent tax credit would benefit lower-middle-income families most - while hurting some upper-income taxpayers. the bite on the better off may be softened some by the reductions in overall tax rates.

The cuts in corporate taxes would help virtually every kind of business, with special breaks for the airlines, utilities and railroads as a result of the changes in the investment tax credit limits. How much it will spur new spending on plant and equipment, however, remains to be seen.